DE102015205676B4 - Supercharged internal combustion engine with exhaust gas turbocharger and additional compressor and method for operating such an internal combustion engine - Google Patents

Abstract

Supercharged internal combustion engine with- an intake system (1) for supplying charge air,- an exhaust gas discharge system for discharging exhaust gas, and- at least one exhaust gas turbocharger (2) which has a turbine (4) arranged in the exhaust gas discharge system and a compressor (4) arranged in the intake system (1). 3), wherein the compressor (3) is equipped with at least one impeller (3d) mounted on a rotatable shaft (3c) in a compressor housing (3e), wherein- an electrically drivable second compressor (5) upstream of the compressor (3) of the at least one exhaust gas turbocharger (2) is arranged in the intake system (1), the second compressor (5) comprising at least one impeller (5d) mounted on a rotatable shaft (5c) in a compressor housing (5e) and being an axial compressor (5b). , whose outlet area (5a) runs coaxially to the shaft (5c) of the second compressor (5), so that the outflow of the charge air from the second compressor (5) via the outlet area (5a) essentially axially takes place, wherein- the electrically drivable second compressor (5) is designed as a switchable compressor (5), characterized in that- the compressor (3) of the at least one exhaust gas turbocharger (2) has an inlet area (3a) which is coaxial with the shaft ( 3c) of the compressor (3) and runs coaxially to the outlet area (5a) of the second compressor (5) and is designed so that the flow of charge air to the compressor (3) of the at least one exhaust gas turbocharger (2) takes place essentially axially, the second compressor (5) is designed for larger volume flows than the compressor (3) of the at least one exhaust gas turbocharger (2), and a third bypass line is provided for the purpose of blowing off the exhaust gas, which branches off from the exhaust gas removal system upstream of the turbine (4).

Description

The invention relates to a supercharged internal combustion engine having the features of the preamble of claim 1.

Furthermore, the invention relates to a method for operating such an internal combustion engine.

In the generic DE 10 2010 023 188 A1 describes a charger for an internal combustion engine, comprising a turbo compressor with at least one compressor impeller and an intake side and a pressure side, a flywheel for storing drive energy, an auxiliary motor for driving the compressor impeller and the flywheel, and a first shut-off element arranged on the intake side of the turbo compressor. This device is intended to provide short-term boost pressure for an internal combustion engine, e.g. B. to bridge a turbo lag of an exhaust gas turbocharger, which is used in an internal combustion engine as a main charger. To this end, it is proposed to constantly drive the compressor impeller of the turbo compressor, to close the first shut-off element in the operating phase in which the charger does not have to provide boost pressure and to evacuate the suction-side compressor air space using the turbo compressor's own compression capacity. In operating phases in which the charger has to provide boost pressure, the first shut-off element is opened and the auxiliary engine is supported in driving the compressor impeller of the turbo compressor by the drive energy stored in the flywheel.

the DE 10 2008 026 025 A1 relates to a drive train, in particular a motor vehicle drive train, with an internal combustion engine that generates an exhaust gas flow. A first exhaust gas turbine and a second exhaust gas turbine are arranged one behind the other in the exhaust gas flow, and/or a first fresh air compressor and a second fresh air compressor are arranged one behind the other in a fresh air flow fed to the internal combustion engine, with the second exhaust gas turbine behind the first exhaust gas turbine and/or the first exhaust gas turbine in the flow direction of the exhaust gas Fresh air compressor is arranged in the flow direction of the fresh air behind the second fresh air compressor. The two exhaust gas turbines are designed as radial turbines in such a way that exhaust gas flows into the first and outflow from the second exhaust gas turbine in the radial direction and exhaust gas flows out of the first and outflow from the second exhaust gas turbine in the axial direction of the respective exhaust gas turbine and/or the direction the inflow of the first fresh air compressor corresponds to the direction of the outflow of the second fresh air compressor.

the EP 1 995 427 A1 relates to a compressor system for internal combustion engines. The compressor system has an additional air compressor for compressing fresh air to be supplied to the internal combustion engine. The boost air compressor includes an electric motor, and this electric motor in turn includes a rotor and a stator with a rotor gap therebetween, the rotor gap having an inlet air opening for the boost air compressor. With the compressor system, an increase in output over the entire speed range of the internal combustion engine should be achievable in a cost-effective manner and with very short reaction times.

A loader according to the U.S. 6,328,024 B 1, using an electric axial compressor or fan, is described with its various connections to an internal combustion engine. A control system is also described to allow the supercharger to be operated from the throttle mechanism to provide additional power through the use of the supercharger when the engine is otherwise operating at its normal (uncontrolled) full power.

the DE 102 13 897 A1 relates to a variable exhaust gas turbocharger for an internal combustion engine with an exhaust gas turbine and a compressor with a variable swirl and/or throttle device. The exhaust gas turbocharger is formed by a housing and a compressor wheel connected to an exhaust gas turbine wheel via a shaft. The compressor has only one inflow duct, in which the variable swirl and throttle device is arranged upstream of the compressor wheel in the direction of flow.

An internal combustion engine of the type mentioned is used as a motor vehicle drive. In the context of the present invention, the term internal combustion engine includes diesel engines and Otto engines, but also hybrid internal combustion engines that use a hybrid combustion process, as well as hybrid drives that, in addition to the internal combustion engine, include an electric machine that can be driven with the internal combustion engine, which takes power from the internal combustion engine or delivers additional power as a switchable auxiliary drive.

In recent years there has been a trend towards small, supercharged engines, with supercharging primarily being a method of increasing performance in which the air required for the engine's combustion process is compressed. The economic importance of these engines for the automotive industry continues to increase.

An exhaust gas turbocharger is often used for charging, in which a compressor and a Turbine are arranged on the same shaft. The hot exhaust gas flow is fed to the turbine and expands in the turbine, releasing energy, causing the shaft to rotate. The energy given off by the exhaust gas flow to the turbine and finally to the shaft is used to drive the compressor, which is also arranged on the shaft. The compressor conveys and compresses the charge air supplied to it, which means that the cylinders are charged. Advantageously, a charge air cooler is provided downstream of the compressor in the intake system, with which the compressed charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thus increases the density of the charge air, so that the cooler also contributes to better filling of the cylinders, ie to a larger air mass. Compression occurs through cooling.

The advantage of an exhaust gas turbocharger compared to a mechanical supercharger is that there is no mechanical connection between the supercharger and the internal combustion engine for power transmission or is required. While a mechanical supercharger draws the energy required for its drive completely from the internal combustion engine and thus reduces the power provided and in this way adversely affects the efficiency, the exhaust gas turbocharger uses the exhaust gas energy of the hot exhaust gases.

As already mentioned, supercharging serves to increase performance. The air required for the combustion process is compressed, which means that a larger air mass can be supplied to each cylinder per working cycle. As a result, the fuel mass and thus the intermediate pressure can be increased.

Supercharging is a suitable means of increasing the performance of an internal combustion engine with the same displacement or reducing the displacement with the same performance. In any case, supercharging leads to an increase in installation space performance and a more favorable mass of power. If the displacement is reduced, the load collective can be shifted towards higher loads, at which specific fuel consumption is lower.

Supercharging consequently supports the constant effort in the development of internal combustion engines to minimize fuel consumption, i. H. to improve the efficiency of the internal combustion engine.

Another fundamental goal is to reduce pollutant emissions. When solving this task, charging can also be expedient. With a targeted design of the supercharging, advantages in terms of efficiency and exhaust emissions can be achieved.

Difficulties are encountered in the design of the exhaust gas turbocharger, with the basic aim being to achieve a noticeable increase in performance in all speed ranges. According to the prior art, however, a sharp drop in torque is observed when the speed falls below a certain level.

This drop in torque becomes understandable when it is taken into account that the boost pressure ratio depends on the turbine pressure ratio. If the engine speed is reduced, this leads to a smaller exhaust gas mass flow and thus to a smaller turbine pressure ratio. Consequently, the boost pressure ratio also decreases towards lower speeds. This is equivalent to a drop in boost pressure or drop in torque.

In practice, the relationships described above often lead to a small exhaust gas turbocharger, i. H. an exhaust gas turbocharger with a small turbine cross-section is used, as a result of which the turbine pressure ratio can be increased. However, this worsens the supercharging at high speeds and only shifts the drop in torque towards lower speeds. In addition, this procedure, i. H. the reduction of the turbine cross-section, since the desired supercharging and increase in performance should be unrestricted and possible to the desired extent even at high speeds.

According to the prior art, attempts are made to improve the torque characteristics of a supercharged internal combustion engine by means of various measures.

For example, through a small design of the turbine cross-section and simultaneous exhaust gas blow-off, the exhaust gas blow-off being able to be controlled by means of boost pressure or by means of exhaust gas pressure. Such a turbine is also referred to as a waste gate turbine. If the exhaust gas mass flow exceeds a critical value, part of the exhaust gas flow is routed past the turbine by means of a bypass line as part of the so-called exhaust gas blow-off. However, as mentioned above, this procedure has the disadvantage that the charging behavior is inadequate at higher speeds.

The torque characteristics of a supercharged internal combustion engine can also be improved by a plurality of turbochargers arranged in parallel, ie by a plurality of turbines with a smaller turbine cross section arranged in parallel turbines are successively switched on as the amount of exhaust gas increases.

The torque characteristics can also be advantageously influenced by means of several exhaust gas turbochargers connected in series. By connecting two exhaust-gas turbochargers in series, of which one exhaust-gas turbocharger serves as the high-pressure stage and one exhaust-gas turbocharger as the low-pressure stage, the engine characteristic map can be expanded in an advantageous manner, both towards smaller compressor flows and towards larger compressor flows.

In particular, in the case of the exhaust gas turbocharger serving as the high-pressure stage, it is possible to shift the surge limit towards smaller compressor flows, as a result of which high boost pressure ratios can be achieved even with small compressor flows, which significantly improves the torque characteristics in the lower speed range. This is achieved by designing the high-pressure turbine for small exhaust gas mass flows and providing a bypass line, with which exhaust gas is increasingly routed past the high-pressure turbine as the exhaust gas mass flow increases. For this purpose, the bypass line branches off from the exhaust gas removal system upstream of the high-pressure turbine and opens back into the exhaust gas removal system upstream of the low-pressure turbine. A shut-off element is arranged in the bypass line in order to control the flow of exhaust gas that is routed past the high-pressure turbine.

However, the use of several exhaust gas turbochargers also has disadvantages, as explained below using two-stage charging.

When designing the exhaust gas turbocharger, efforts are made to place the turbine or turbines as close as possible to the outlet of the internal combustion engine, i. H. near the outlet openings of the cylinders, in order to be able to optimally use the exhaust gas enthalpy of the hot exhaust gases, which is largely determined by the exhaust gas pressure and the exhaust gas temperature, and to ensure a fast response behavior of the turbocharger. Arrangement close to the engine not only shortens the path of the hot exhaust gases to the turbine, but also reduces the volume of the exhaust gas removal system upstream of the turbine. The thermal inertia of the exhaust gas evacuation system also decreases by reducing the mass and length of the exhaust gas evacuation system section up to the turbine.

For the reasons mentioned above, the turbines are usually arranged on the outlet side of the cylinder head. According to the state of the art, the exhaust manifold is often integrated in the cylinder head. The integration of the exhaust manifold also allows the drive unit to be packaged tightly. In addition, a liquid cooling system that may be provided in the cylinder head can participate, so that the manifold does not have to be made from materials that can be subjected to high thermal loads and are cost-intensive.

Naturally, with two-stage turbocharging, the arrangement of the turbine close to the engine causes major problems for the low-pressure stage. It should also be taken into account that the turbine of an exhaust gas turbocharger is usually designed in a radial manner, i. H. the flow towards the rotor blades is essentially radial. In the context of the present invention, essentially radial means that the speed component in the radial direction is greater than the axial speed component. The velocity vector of the flow intersects the shaft of the exhaust gas turbocharger at a right angle if the flow is exactly radial.

Consequently, after flowing through the high-pressure turbine, the exhaust gas must first be diverted or deflected via the exhaust gas discharge system in order to be able to be fed to the low-pressure stage downstream of the radial turbine. This significantly increases not only the travel distance, but also the volume and thermal inertia between the two turbines.

In order to be able to use the exhaust gas energy as efficiently as possible, the exhaust gas should be deflected as little as possible. Every change in direction of the exhaust gas flow, for example as a result of a bend in the exhaust gas discharge system, results in a pressure loss in the exhaust gas flow and thus in an enthalpy loss. However, everything should be avoided that reduces the pressure in the exhaust gas and reduces the exhaust gas energy still available at the turbine.

In order to be able to flow radially onto the rotor blades, the inlet area for supplying the exhaust gas is designed according to the prior art as a spiral or worm housing running all around, so that the exhaust gas flows to the turbine essentially radially. Such a radial turbine is, for example, in the EP 1 710 415 A1 described.

Feeding the exhaust gas to the low-pressure turbine by means of a spiral or screw housing requires the exhaust gas or the exhaust gas flow to be deflected multiple times with large changes in direction. As already explained, however, every change in direction causes a pressure loss in the exhaust gas flow, which is why less energy can be extracted from the exhaust gas at the low-pressure turbine.

Occasionally, the low-pressure turbine of an exhaust gas turbocharger is also designed as an axial turbine, ie the flow towards the impeller blades is essentially axial. In the context of the present invention, essentially axial means that the speed component in the axial direction is greater than the radial speed component. The velocity vector of the inflow in the area of the impeller preferably runs parallel to the shaft of the exhaust gas turbocharger if the inflow runs exactly axially.

According to the prior art, however, the inlet area for supplying the exhaust gas is often designed as a spiral or worm housing running all around, even in axial turbines, so that at least in the inlet area the flow of the exhaust gas runs or is guided obliquely or radially to the shaft, for which purpose a deflection is required of the exhaust gas between the turbines is or will be required. Losses in the exhaust gas enthalpy available at the turbine wheel have to be accepted. the EP 1 710 415 A1 describes such an axial turbine.

What has been said for the turbines also applies analogously to the compressors of the exhaust gas turbochargers, with the compressors also being arranged on the outlet side due to the arrangement of the turbines on the outlet side and the charge air compressed in the compressors first having to be routed downstream of the compressors to the inlet side of the cylinder head in order to to be fed to the cylinders. Unlike turbines, compressors are defined by their outflow. A centrifugal compressor is therefore a compressor whose outflow from the rotor blades is essentially radial. In contrast, the outflow from the impeller blades of an axial compressor is essentially axial.

In order to avoid a pressure loss on the intake side or to minimize the pressure loss, the charge air should be deflected as little as possible. The intake system should be as short as possible and have as few changes in direction upstream of the compressors, downstream of the compressors and between the compressors as possible.

In this respect, multiple deflection of the charge air flow with large changes in direction for the purpose of transferring the charge air to the inlet side of the cylinder head and feeding it to the compressors is to be regarded as disadvantageous. This is detrimental to maintaining pressure, particularly in the compressed charge air.

The use of several exhaust gas turbochargers also has disadvantages in terms of tight packaging of the drive unit in the engine compartment, in particular also due to the complex exhaust pipe system.

Against this background, it is an object of the present invention to provide a supercharged internal combustion engine according to the preamble of claim 1, with which the disadvantages known from the prior art are overcome, whose charging behavior is improved and whose charging requires less space.

A further sub-task of the present invention is to indicate a method for operating such an internal combustion engine.

• - einem Ansaugsystem zum Zuführen von Ladeluft,
• - einem Abgasabführsystem zum Abführen von Abgas, und
• - mindestens einem Abgasturbolader, der eine im Abgasabführsystem angeordnete Turbine und einen im Ansaugsystem angeordneten Verdichter umfasst, wobei der Verdichter mit mindestens einem in einem Verdichtergehäuse auf einer drehbaren Welle gelagerten Laufrad ausgestattet ist, wobei
• - ein elektrisch antreibbarer zweiter Verdichter stromaufwärts des Verdichter des mindestens einen Abgasturboladers im Ansaugsystem angeordnet ist, wobei der zweite Verdichter mindestens ein in einem Verdichtergehäuse auf einer drehbaren Welle gelagertes Laufrad umfasst und ein Axialverdichter ist, dessen Austrittsbereich koaxial zur Welle des zweiten Verdichters verläuft, so dass die Abströmung der Ladeluft aus dem zweiten Verdichter via Austrittsbereich im Wesentlichen axial erfolgt, wobei
• - der elektrisch antreibbare zweite Verdichter als zuschaltbarer Verdichter ausgebildet ist.

The first subtask is solved by a supercharged internal combustion engine

• - an intake system for supplying charge air,
• - an exhaust gas discharge system for discharging exhaust gas, and
• - At least one exhaust gas turbocharger, which comprises a turbine arranged in the exhaust gas discharge system and a compressor arranged in the intake system, the compressor being equipped with at least one impeller mounted on a rotatable shaft in a compressor housing, wherein
• - An electrically drivable second compressor is arranged upstream of the compressor of the at least one exhaust gas turbocharger in the intake system, the second compressor comprising at least one impeller mounted on a rotatable shaft in a compressor housing and being an axial compressor whose outlet area runs coaxially with the shaft of the second compressor, see above that the discharge of the charge air from the second compressor via the outlet area is essentially axial, wherein
• - The electrically drivable second compressor is designed as a switchable compressor.

• - der Verdichter des mindestens einen Abgasturboladers einen Eintrittsbereich aufweist, der koaxial zur Welle des Verdichters und koaxial zum Austrittsbereich des zweiten Verdichters verläuft und ausgebildet ist, so dass die Anströmung der Ladeluft zu dem Verdichter des mindestens einen Abgasturboladers im Wesentlichen axial erfolgt, wobei
• - der zweite Verdichter größer, also auf größere Volumenströme ausgelegt ist als der Verdichter des mindestens einen Abgasturboladers, und
• - zum Zwecke der Abgasabblasung eine dritte Bypassleitung vorgesehen ist, die stromaufwärts der Turbine vom Abgasabführsystem abzweigt.

According to the invention it is proposed that

• - the compressor of the at least one exhaust gas turbocharger has an inlet area which runs coaxially to the shaft of the compressor and coaxially to the outlet area of the second compressor and is designed such that the charge air flows to the compressor of the at least one exhaust gas turbocharger essentially axially, wherein
• - the second compressor is larger, ie designed for larger volume flows, than the compressor of the at least one exhaust gas turbocharger, and
• - A third bypass line is provided for the purpose of exhaust gas blow-off, which is upstream branches off from the exhaust gas discharge system towards the turbine.

The terms "first", "second", "third", etc. used in this specification are for the purpose of distinction only. In particular, no order or priority of the objects mentioned in connection with these terms should be implied by their use.

The internal combustion engine according to the invention charged by means of an exhaust gas turbocharger is equipped with an additional compressor of axial design, which is arranged upstream of the compressor of the at least one exhaust gas turbocharger in the intake system.

This second compressor also has an outlet area that runs coaxially to the shaft of the compressor, so that the charge air flows out of this additional compressor essentially axially. Consequently, after flowing through the second compressor, the charge air does not have to be deflected in order to be fed to the compressor of the at least one exhaust gas turbocharger. Since the charge air flow is not deflected or changed in direction, unnecessary pressure losses in the charge air flow as a result of flow deflection are avoided and the precompressed charge air can be further compressed in the compressor of the exhaust gas turbocharger. The efficiency and boost pressure ratio of the two-stage compression can be increased as a result.

The use of an axial compressor instead of a further exhaust gas turbocharger together with the outlet area designed according to the invention allows tight packaging, in particular a reduction in the distance, the volume and the mass of the intake system between the two compressors.

The effects and technical effects described above are further supported and made possible by the fact that the compressor of the at least one exhaust gas turbocharger has an inlet area which runs coaxially with the shaft of the compressor and coaxially with the outlet area of the second compressor and is designed such that the charge air flows towards the compressor of the at least one exhaust gas turbocharger takes place essentially axially.

The second compressor is an electrically drivable compressor, so that there is no mechanical connection for power transmission between the compressor and the internal combustion engine or is required, which is why the second compressor requires little space and allows dense packaging of the supercharging or the internal combustion engine. In addition, the second compressor is designed as a switchable compressor, which is switched on only when necessary for the purpose of precompression of the charge air if two-stage compression is carried out.

According to the invention, the second compressor is designed to be larger than the compressor of the at least one exhaust gas turbocharger, i. H. designed for larger volume flows.

With two series-connected compressors arranged in the intake system, it is advantageous to design the second compressor to be larger than the downstream compressor of the exhaust gas turbocharger, since with two-stage compression the compressor of the charger forms the high-pressure stage and compresses the charge air, which is already present in the then Was supercharged serving low-pressure stage second compressor.

The second compressor is designed to be larger than the compressor of the at least one exhaust gas turbocharger and, as a low-pressure stage, takes over the pre-compression of the charge air as part of a two-stage compression with large amounts of charge air, ie at higher engine speeds n _mot . The compressor of the at least one exhaust gas turbocharger is designed to be smaller and manages the compression of the charge air with small or medium-sized quantities of charge air. In the case of small or medium-sized amounts of charge air, the second compressor could then be bypassed by means of a bypass line and the compressor of the at least one exhaust gas turbocharger could compress the charge air as part of a single-stage compression.

For the reasons mentioned above, a bypass line is also provided according to the invention for the purpose of blowing off exhaust gas, which branches off from the exhaust gas discharge system upstream of the turbine of the at least one exhaust gas turbocharger and is referred to as the third bypass line.

The provision of a bypass line allows the turbine or the high-pressure turbine to be designed for small or medium-sized exhaust gas mass flows and thus for the lower or medium part-load range.

The smaller turbine cross-section ensures a higher turbine pressure ratio for small and medium-sized amounts of exhaust gas and thus a higher boost pressure ratio on the compressor side and a higher boost pressure for small and medium-sized amounts of charge air.

With the internal combustion engine according to the invention, the first object on which the invention is based is achieved, namely a supercharged one Internal combustion engine provided with which the disadvantages known from the prior art are overcome, the charging behavior is improved and the charging has a smaller space requirement.

Further advantageous embodiments of the internal combustion engine are discussed in connection with the subclaims.

Embodiments of the internal combustion engine are advantageous in which the compressor of the at least one exhaust gas turbocharger is a radial compressor. This embodiment allows tight packaging of the exhaust gas turbocharger and thus of the charging system as a whole. The compressor housing can be designed as a spiral or snail housing, whereby the deflection of the charge air flow in the compressor of the exhaust gas turbocharger can be used in an advantageous manner to direct the compressed charge air over the shortest path from the outlet side, on which the turbine of the exhaust gas turbocharger is arranged, to the inlet side respectively.

Embodiments of the internal combustion engine are advantageous in which the turbine of the at least one exhaust gas turbocharger is a radial turbine. This embodiment also allows tight packaging of the exhaust gas turbocharger and thus of the charging system as a whole.

For reasons of packaging, embodiments of the internal combustion engine in which only one exhaust gas turbocharger is provided are also advantageous.

Embodiments of the internal combustion engine are advantageous in which the second compressor has an inlet region which runs coaxially to the shaft of the second compressor and is designed such that the charge air flows essentially axially to the second compressor. This embodiment facilitates the arrangement of the at least one impeller in the compressor housing of the second compressor and the design of the electric drive.

Such a drive is, for example, in the German Offenlegungsschrift DE 100 40 122 A1 described and discussed. In this way, an electric motor, ie an electric drive, can be formed which comprises a rotor which is connected in a torque-proof manner to the compressor impeller and a stator which is fixed to the housing and which radially surrounds the rotor. The rotor made of a magnetic material is preferably ring-shaped and sits on the radially outer edge of the compressor impeller. When the stator, preferably a coil, is energized, an electromagnetic force that rotates the rotor is generated.

The compressor impeller can also be divided into two areas, namely an auxiliary impeller, which forms the rotor, and a main impeller, which includes the shaft hub and the rotor blades of the compressor impeller. The auxiliary rotor wheel is arranged upstream of the main rotor wheel.

Embodiments of the internal combustion engine are advantageous in which the turbine of the at least one exhaust gas turbocharger has a variable turbine geometry.

Variable turbine geometry increases charging flexibility. It allows a stepless adjustment of the turbine geometry to the respective operating point of the internal combustion engine, in particular to the current exhaust gas mass flow. In contrast to a turbine with a fixed geometry, the turbine does not have to be designed strictly for a specific amount of exhaust gas, which is why the turbine ensures satisfactory supercharging over a wide speed and load range, namely the desired boost pressure on the inlet side.

Embodiments of the internal combustion engine are advantageous in which a first bypass line is provided which has a shut-off element and which branches off from the intake system upstream of the second compressor and opens back into the intake system between the compressors.

In the case of small amounts of charge air or low speeds, the compressor of the at least one exhaust gas turbocharger primarily takes over the compression of the charge air, which is why the second compressor is preferably bypassed by means of the first bypass line. At higher speeds, i. H. with larger amounts of charge air, the second compressor ensures the pre-compression of the charge air as part of a two-stage turbocharger, which is why the first bypass line should then preferably be closed.

As a rule, however, the second compressor will not present an excessive flow resistance with small amounts of charge air, which is why a first bypass line will not be necessary under all circumstances.

Embodiments of the internal combustion engine are advantageous in which the compressor of the at least one exhaust gas turbocharger has a variable compressor geometry.

A variable compressor geometry is particularly advantageous if the turbine of the exhaust gas turbocharger has a variable turbine geometry and a variable compressor geometry can then be continuously adjusted to the turbine geometry.

In particular, if only a small exhaust gas mass flow is passed through the turbine, a variable compressor geometry proves to be advantageous, since the surge limit of the compressor in the compressor map can be shifted towards small compressor flows by adjusting the blades, thus avoiding the compressor working beyond the surge limit .

Embodiments of the internal combustion engine are advantageous in which a second bypass line is provided which has a shut-off element and which branches off from the intake system upstream of the compressor of the at least one exhaust gas turbocharger and re-enters the intake system downstream of the compressor of the at least one exhaust gas turbocharger.

The second bypass line makes it possible to bypass the compressor of the at least one exhaust gas turbocharger.

Embodiments of the internal combustion engine are advantageous in which the third bypass line opens back into the exhaust gas discharge system downstream of the turbine, with a shut-off element being provided in the third bypass line to control the exhaust gas discharge. With regard to bypassing the turbine using a bypass line, it has already been explained. Reference is made to the corresponding statements.

Embodiments of the internal combustion engine are advantageous in which a guide device is arranged in the outlet region of the second compressor downstream of the at least one impeller of the second compressor. The velocity vector of the oncoming flow in the area of the at least one impeller of the compressor of the exhaust gas turbocharger preferably also has a radial component to the shaft, which increases the efficiency.

Therefore, embodiments of the internal combustion engine are also advantageous in which a guide device is provided in the inlet area upstream of the at least one impeller of the compressor of the exhaust gas turbocharger.

In this context, embodiments of the internal combustion engine in which the guide device is mounted in the outlet region of the second compressor are advantageous.

In this connection, embodiments of the internal combustion engine in which the guide device accommodates the shaft of the second compressor for the purpose of storage are also advantageous.

Embodiments of the internal combustion engine are advantageous in which a holder for the purpose of supporting the shaft of the second compressor is arranged upstream of the at least one impeller of the second compressor.

Embodiments of the internal combustion engine are advantageous in which an intercooler is arranged in the intake system downstream of the compressor. The intercooler lowers the air temperature and thus increases the density of the charge air, which also means that the cooler can be used to better fill the combustion chamber with air, i. H. contributes to a larger air mass.

Embodiments of the internal combustion engine are advantageous in which a section of the intake system provided between the outlet area of the second compressor and the inlet area of the compressor of the at least one exhaust gas turbocharger tapers.

This is advantageous with regard to a two-stage compression of the charge air, in which the density of the charge air is already increased upstream of the compressor of the exhaust gas turbocharger.

Embodiments of the internal combustion engine are advantageous in which the shut-off element in the first, second and/or third bypass line is a valve or a throttle valve.

Embodiments are advantageous in which the shut-off element can be controlled electrically, hydraulically, pneumatically, mechanically or magnetically, preferably by means of a motor control.

Embodiments of the supercharged internal combustion engine in which exhaust gas recirculation is provided are advantageous.

In this context, embodiments of the supercharged internal combustion engine are advantageous in which exhaust gas recirculation is provided, which includes a line that branches off from the exhaust gas discharge system upstream of the turbine and opens into the intake system, preferably downstream of the compressor.

In order to comply with future limit values for nitrogen oxide emissions, exhaust gas recirculation is increasingly being used, ie the recirculation of exhaust gases from the outlet side to the inlet side, in which the nitrogen oxide emissions can be significantly reduced as the exhaust gas recirculation rate increases. The exhaust gas recirculation rate x _AGR is determined with x _AGR = m _AGR / (m _AGR + m _{fresh air} ), where m _AGR is the mass of recirculated exhaust gas and m _{fresh air} is the supplied fresh air - possibly guided and compressed by a compressor referred to as air or combustion air. Exhaust gas recirculation is also suitable for reducing emissions of unburned hydrocarbons in the partial load range. In order to achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates are required.

Embodiments are advantageous in which the line for exhaust gas recirculation opens into the intake system downstream of an intercooler. In this way, the exhaust gas flow is not routed through the intercooler and consequently cannot contaminate this cooler with deposits of pollutants contained in the exhaust gas flow, in particular soot particles and oil.

Embodiments are advantageous in which an additional cooler is provided in the exhaust gas recirculation line. This additional cooler lowers the temperature in the hot exhaust gas flow and thus increases the density of the exhaust gases. As a result, the temperature of the cylinder fresh charge, which occurs when the fresh air is mixed with the recirculated exhaust gases, is further reduced, which means that the additional cooler also contributes to better filling of the combustion chamber with charge air.

Embodiments are advantageous in which a shut-off element is provided in the exhaust gas recirculation line. This shut-off element is used to control the exhaust gas recirculation rate.

Also advantageous are embodiments of the supercharged internal combustion engine in which exhaust gas recirculation is provided, which includes a line that branches off from the exhaust gas discharge system downstream of the turbine and opens into the intake system, preferably upstream of the compressor.

In contrast to the already mentioned high-pressure EGR, which extracts exhaust gas from the exhaust gas removal system upstream of the turbine and introduces it into the intake system downstream of the compressor, low-pressure EGR returns exhaust gas that has already flowed through the turbine to the inlet side. For this purpose, the low-pressure EGR includes a recirculation line, which branches off from the exhaust gas discharge system downstream of the turbine and opens into the intake system upstream of the compressor.

The exhaust gas, which is returned to the inlet side by means of low-pressure EGR and is preferably cooled, is mixed with fresh air upstream of the compressor. The mixture of fresh air and recirculated exhaust gas generated in this way forms the charge air, which is fed to the compressors and compressed.

It is harmless that exhaust gas is passed through the compressor as part of the low-pressure EGR, since exhaust gas is generally used which has been subjected to exhaust gas aftertreatment downstream of the turbine, in particular in the particle filter. Deposits in the compressor, which change the geometry of the compressor, in particular the flow cross sections, and in this way impair the efficiency of the compressor, are therefore not to be feared.

The second sub-task on which the invention is based, namely to show a method for operating an internal combustion engine of the type described above, is achieved by a method which is characterized in that the second compressor is switched on as soon as the speed n _mot of the internal combustion engine reaches a predetermined speed n _threshold,1 is exceeded and/or a higher torque is requested, so that the charge air is compressed as part of a two-stage compression.

What has already been said for the internal combustion engine according to the invention also applies to the method according to the invention, which is why reference is generally made at this point to the statements made above with regard to the supercharged internal combustion engine. The various internal combustion engines sometimes require different process variants.

In the present case, the second compressor serves to pre-compress the charge air in the case of larger quantities of charge air or higher speeds, i. H. to improve the torque characteristics in the upper speed range. In the case of smaller amounts of charge air or lower speeds, the second compressor could then be bypassed by means of the first bypass line and the compressor of the at least one exhaust gas turbocharger ensures compression of the charge air as part of a single-stage supercharging.

In the case of internal combustion engines in which a first bypass line is provided which has a shut-off element and which branches off from the intake system upstream of the second compressor and opens back into the intake system between the compressors, method variants are therefore also advantageous which are characterized in that the first bypass line is open is as soon as the speed n _mot of the internal combustion engine falls below a predefinable speed n _threshold,2 .

Method variants in which the third bypass line is opened as soon as the amount of exhaust gas exceeds a definable amount of exhaust gas are also advantageous.

• 1 schematisch die Aufladung einer ersten Ausführungsform der Brennkraftmaschine, teilweise geschnitten.

In the following, the invention is based on an exemplary embodiment 1 described in more detail. This shows:

• 1 schematically the supercharging of a first embodiment of the internal combustion engine, partially sectioned.

1 shows schematically the supercharging of a first embodiment of the supercharged internal combustion engine, partially in section.

The internal combustion engine has an intake system 1 for supplying the charge air to the cylinders. An exhaust gas turbocharger 2 is provided for the purpose of charging the cylinders. The turbine 4 is a radial turbine 4a and the compressor 3 is a radial compressor 3b, in the housing 3e of which an impeller 3d is mounted on a rotatable shaft 3c.

To support charging if necessary and to improve the torque characteristics, an electrically drivable second compressor 5 is arranged in the intake system 1 upstream of the compressor 3 of the exhaust gas turbocharger 2, in whose compressor housing 5e an impeller 5d is mounted on a rotatable shaft 5c. This second compressor 5 is an axial compressor 5b, the inlet area 5g or outlet area 5a of which runs coaxially to the shaft 5c of the second compressor 5 and is designed so that both the inflow of the charge air to the second compressor 5 and the outflow of the charge air from the second Compressor 5 takes place essentially axially.

A guide device 5f is arranged in the outlet region 5a of the second compressor 5 downstream of the impeller 5d of the second compressor 5 . The guide device 5f also accommodates the shaft 5c of the second compressor 5 for the purpose of bearing, with a bracket 5h arranged upstream of the impeller 5d supplementing the bearing of the shaft 5c of the second compressor 5.

The compressor 3 of the exhaust gas turbocharger 2 has an inlet area 3a, which runs coaxially to the shaft 3c of the compressor 3 and coaxially to the outlet area 5a of the second compressor 5 and is designed so that the charge air flows to the compressor 3 of the exhaust gas turbocharger 2 essentially axially takes place and the section 6 of the intake system 1 between the compressors 3, 5 is comparatively short and small in volume and has no changes in direction.

The second compressor 5 is electrically driven and switched on if necessary, the electric drive, i. H. the electric motor is formed using a rotor 8b which is connected in a rotationally fixed manner to the compressor impeller 5d and a stator 8a which is fixed to the housing and which radially surrounds the rotor 8b.

The rotor 8b made of a magnetic material is ring-shaped and sits on the radially outer edges of the compressor impeller blades. When the stator 8a, a coil, is energized, an electromagnetic force rotating the rotor 8b is generated.

The compressor 3 of the exhaust gas turbocharger 2 is designed to be smaller than the second compressor 5, which is only switched on when necessary. In the present case, the second compressor 5 takes over the pre-compression of the charge air at higher speeds, i. H. in the upper speed range. At lower speeds, the compressor 3 of the exhaust gas turbocharger 2 ensures the compression of the charge air as part of a single-stage supercharging, with the second compressor 5 using a bypass line 7, which branches off from the intake system 1 upstream of the second compressor 5 and between the compressors 3, 5 back into the Intake system 1 opens, can be bypassed. A flap 7b serving as a shut-off element 7a is provided at the inlet of this first bypass line 7 .

Reference List

1

Ansaugsystem

2

Abgasturbolader

3

Verdichter des Abgasturboladers

3a

Eintrittsbereich des Verdichters des Abgasturboladers

3b

Radialverdichter

3c

Welle des Verdichters des Abgasturboladers

3d

Laufrad des Verdichters des Abgasturboladers

3e

Verdichtergehäuse des Abgasturboladers

4

Turbine des Abgasturboladers

4a

Radialturbine

5

zweiter Verdichter

5a

Austrittsbereich des zweiten Verdichters

5b

Axialverdichter

5c

Welle des zweiten Verdichters

5d

Laufrad des zweiten Verdichters

5e

Verdichtergehäuse des zweiten Verdichters

5f

Leiteinrichtung

5g

Eintrittsbereich des zweiten Verdichters

5h

Halterung

6

Abschnitt des Ansaugsystems, Zwischenstück

7

erste Bypassleitung

7a

Absperrelement

7b

Klappe

8a

Stator

8b

Rotor

Abkürzungsverzeichnis

AGR

Abgasrückführung

mAGR

Masse an zurückgeführtem Abgas

mFrischluft

Masse an zugeführter Frischluft bzw. Ladeluft

nmot

Drehzahl der Brennkraftmaschine

nthreshold,1

vorgebbare Drehzahl für das Zuschalten des zweiten Verdichters

xAGR

Abgasrückführrate

1

intake system

2

exhaust gas turbocharger

3

Compressor of the exhaust gas turbocharger

3a

Inlet area of the compressor of the exhaust gas turbocharger

3b

centrifugal compressor

3c

Compressor shaft of the exhaust gas turbocharger

3d

Impeller of the compressor of the exhaust gas turbocharger

3e

Compressor housing of the exhaust gas turbocharger

4

Turbine of the exhaust gas turbocharger

4a

radial turbine

5

second compressor

5a

Outlet area of the second compressor

5b

axial compressor

5c

Shaft of the second compressor

5d

Impeller of the second compressor

5e

Compressor housing of the second compressor

5f

control device

5g

Entry area of the second compressor

5h

bracket

6

Intake system section, intermediate piece

7

first bypass line

7a

shut-off element

7b

flap

8a

stator

8b

rotor

List of abbreviations

EGR

exhaust gas recirculation

MAGR

Mass of recirculated exhaust gas

mfresh air

Mass of supplied fresh air or charge air

nmot

speed of the internal combustion engine

threshold,1

Predeterminable speed for switching on the second compressor

xEGR

exhaust gas recirculation rate

Claims (17)

Supercharged internal combustion engine with - an intake system (1) for supplying charge air, - an exhaust gas discharge system for discharging exhaust gas, and - at least one exhaust gas turbocharger (2), which has a turbine (4) arranged in the exhaust gas discharge system and a compressor (4) arranged in the intake system (1). 3), wherein the compressor (3) is equipped with at least one impeller (3d) mounted on a rotatable shaft (3c) in a compressor housing (3e), wherein - an electrically drivable second compressor (5) upstream of the compressor (3) of the at least one exhaust gas turbocharger (2) is arranged in the intake system (1), the second compressor (5) comprising at least one impeller (5d) mounted on a rotatable shaft (5c) in a compressor housing (5e) and being an axial compressor (5b). , whose outlet area (5a) runs coaxially to the shaft (5c) of the second compressor (5), so that the outflow of the charge air from the second compressor (5) via the outlet area (5a) essentially a xial takes place, wherein - the electrically drivable second compressor (5) is designed as a switchable compressor (5), characterized in that - the compressor (3) of the at least one exhaust gas turbocharger (2) has an inlet area (3a) which is coaxial to the shaft (3c) of the compressor (3) and runs coaxially to the outlet area (5a) of the second compressor (5) and is designed so that the charge air flows towards the compressor (3) of the at least one exhaust gas turbocharger (2) essentially axially, - the second compressor (5) is designed for larger volume flows than the compressor (3) of the at least one exhaust gas turbocharger (2), and - a third bypass line is provided for the purpose of blowing off the exhaust gas, which branches off from the exhaust gas removal system upstream of the turbine (4). Supercharged internal combustion engine claim 1 , characterized in that the compressor (3) of the at least one exhaust gas turbocharger (2) is a radial compressor (3b). Supercharged internal combustion engine claim 1 or 2 , characterized in that the turbine (4) of the at least one exhaust gas turbocharger (2) is a radial turbine (4a). Supercharged internal combustion engine according to one of the preceding claims, characterized in that the second compressor (5) has an inlet area (5g) which runs coaxially to the shaft (5c) of the second compressor (5) and is designed so that the onflow of the charge air the second compressor (5) takes place essentially axially. Supercharged internal combustion engine according to one of the preceding claims, characterized in that the turbine (4) of the at least one exhaust gas turbocharger (2) has a variable turbine geometry. Supercharged internal combustion engine according to one of the preceding claims, characterized in that a first bypass line (7) is provided which has a shut-off element (7a) and which branches off from the intake system (1) upstream of the second compressor (5) and between the compressors (3, 5) flows back into the intake system (1). Supercharged internal combustion engine according to one of the preceding claims, characterized in that the compressor (3) of the at least one exhaust gas turbocharger (2) has a variable compressor geometry. Supercharged internal combustion engine according to one of the preceding claims, characterized in that a second bypass line is provided which has a shut-off element and which branches off from the intake system (1) upstream of the compressor (3) of the at least one exhaust gas turbocharger (2) and downstream of the compressor (3) of the at least one exhaust gas turbocharger (2) flows back into the intake system (1). Supercharged internal combustion engine according to one of the preceding claims, characterized in that the third bypass line opens out again into the exhaust gas discharge system downstream of the turbine (4) of the at least one exhaust gas turbocharger (2), a shut-off element being provided in the third bypass line to control the exhaust gas discharge. Supercharged internal combustion engine according to one of the preceding claims, characterized in that a guide device (5f) is arranged in the outlet region (5a) of the second compressor (5) downstream of the at least one impeller (5d) of the second compressor (5). Supercharged internal combustion engine claim 10 , characterized in that the guide device (5f) is mounted in the outlet area (5a) of the second compressor (5). Supercharged internal combustion engine claim 10 or 11 , characterized in that the guide device (5f) receives the shaft (5c) of the second compressor (5) for the purpose of storage. Supercharged internal combustion engine according to one of the preceding claims, characterized in that upstream of the at least one impeller (5d) of the second compressor (5) there is a bracket (5h) for the purpose of supporting the shaft (5c) of the second compressor (5). Supercharged internal combustion engine according to one of the preceding claims, characterized in that a charge air cooler is arranged in the intake system (1) downstream of the compressor (3, 5). Supercharged internal combustion engine according to one of the preceding claims, characterized in that a section (6) of the Intake system (1) tapers. Method for operating a supercharged internal combustion engine according to one of the preceding claims, characterized in that the second compressor (5) is switched on as soon as the speed n _mot of the internal combustion engine exceeds a predefinable speed n _threshold,1 in order to increase the charge air as part of a two-stage compression condense. procedure after Claim 16 , characterized in that the third bypass line is opened as soon as the amount of exhaust gas exceeds a predetermined amount of exhaust gas.

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